The invention relates to an energy recovery rectifier device for connection to an AC (alternating current) system. The energy recovery rectifier device comprises an energy recovery rectifier and is in particular a constituent part of an industrial plant. The invention further relates to a method for operating an energy recovery rectifier device and to an industrial plant comprising an energy recovery rectifier device.
Industrial plants typically have a plurality of drives, each of which comprises an electric motor. In such an arrangement, the motor is supplied with electrical power by means of a power converter comprising a rectifier, a DC (direct current) link and an inverter. The inverter is operated in electrical contact with the electric motor and serves to adjust the rotational speed and power output of the electric motor. The rectifier, in contrast, is connected to an AC system or network that has three phases, each of which conducts an alternating current, the individual phases typically being offset from one another by 120°. In the simplest embodiment, the rectifier comprises six diodes that are contacted to one another in an arrangement known as a bridge circuit. Connected in parallel with the rectifier side of the bridge circuit is a DC link capacitor by means of which the DC link voltage present between the rectifier and the inverter is intended to be stabilized.
During operation of the industrial plant there occur time windows within which the electric motor is required to be braked. In order to ensure a comparatively efficient operation of the industrial plant, the electric motor is in this case operated in a generator mode and consequently rotational energy is converted into electrical energy. The DC link capacitor is fed by means of said energy. In a development, the rectifier is embodied with energy recovery capability, such that the recovered electrical energy is fed back again into the AC system and as a result is available to other electricity-consuming loads of the AC system. This enables the DC link capacitor to be dimensioned into a smaller physical size.
In order to embody the rectifier with energy recovery capability, the diodes are bridged by means of semiconductor switches, which are therefore connected in parallel therewith. The electrical current is fed into that phase of the three phases of the AC system that has the highest voltage in order to enable the greatest possible transfer of energy. As a result, a comparatively large electrical current is switched at the time at which a switchover (commutation) takes place from one phase to another phase. A formation of undesirable oscillations within the fed-back current is also possible due to the comparatively abrupt switching and due to any inductances that may be present.
The object underlying the invention is to disclose a particularly suitable energy recovery rectifier device as well as a particularly suitable method for operating an energy recovery rectifier device, and also a particularly suitable industrial plant comprising an energy recovery rectifier device, wherein a formation of oscillations within the fed-back current during operation is preferably reduced.